Distribution of prostheses position after primary total knee arthroplasty on dominant and non-dominant sides

【 Abstract 】 Background To investigate the changes of prosthesis position after primary total knee arthroplasty (TKA) on the dominant and non-dominant sides. Methods A retrospective analysis was made of 132 patients (148 knees) who underwent primary TKA from December 2016 to December 2018 in our hospital. The patients were divided into dominant group (right side) and non-dominant group (left side) according to the position of the three right-handed surgeons. Total operation time, posterior distal femur angle (PDFA), posterior proximal tibia angle (PPTA), malposition rate of femoral prostheses in sagittal, postoperative hip-knee-ankle angle (HKA), mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA) were compared between the two groups. Results The mean total operation time was in dominant group was 111.8(111.8±26.9) and in non-dominant group was 113.7(113.7±26.1) ( P >0.05). Postoperative sagittal alignment, the mean PDFA was 90.2(90.2°±3.3°) in dominant group and 88.8(88.8°±3.6°) in non-dominant group ( P <0.05). The mean PPTA was 84.8(84.8°±2.8°) in dominant group and 85.4(85.4°±3.7°) in non-dominant group ( P >0.05). The incidence of malposition of sagittal femoral prosthesis in dominant group was 6/76 (7.9%) tibia angle; mLDFA: mechanical lateral distal femoral angle; mMPTA: mechanical medial proximal tibial angle; PACS: picture archiving and communication system; BMI: body mass index; ICC: interclass correlation coefficient; THA: total hip arthroplasty.

Total Knee Arthroplasty (TKA) is an effective method for the treatment of end-stage knee arthritis, and ensuring the accurate positioning and alignment of knee components has been considered associated with good stability and a lower rate of loosening 1; 2 . Most of studies focus on improving the accuracy of prosthesis placement including computer-assisted navigation systems, robotic-assisted systems, and patient-specific instrumentation during the past decade 3 .
But there are few studies about the influence of dominant side of the surgeon. Moloney et al. 4  We prospectively followed up and retrospectively reviewed 531 consecutive patients (531 knees) who accepted primary total knee arthroplasties from May 2016 to December 2018. (Fig.1).The TKAs were performed by 3 surgeons(A, B, and C),who were defined as right-handers according to the Edinbuegh Handedness Inventory 8 . The annual operation volume of surgeons were more than 50 TKAs/year 9 . All patients were placed in the supine position, the surgeons performed the surgical procedure standing on the side of the operative extremity. We defined the right-handed surgeons performed the right knee replacement as the dominant side, and the left knee replacement performed by right-handed surgeons was defined as the non-dominant side.
All operations were performed through the medial incision of the knee joint and medial paraptellar approach, the patellofemoral joint was exposed after turning outward the patella, The distal femoral was cut using intramedullary rods and the proximal tibial using extramedullary alignment guides. A posterior reference point of the femur was used as a guide to determine the position of the femoral component in the sagittal plane. Cemented, posterior-stabilized T KAs were performed after use of a measured resection technique. The operation time was recorded from incision to skin closure. All patients stayed until the surgical suture was removed.
Patient demographics, diagnosis, degree of deformity, surgeon, side, prosthesis type, total operation time, complications were recorded. Radiographic analysis was performed on full-length standing anteroposterior radiograph of the lower extremity and adequate lateral radiographs using a picture archiving and communication system (PACS) measurement tools on the earliest acceptable postoperative images. Radiographs were measured by two independent observers who had no clinical contact with the patients.
The following angles were used for descriptive analys is of pre-and postoperative alignment: The hip-knee-ankle angle (HKA) was defined as the angle between the femoral mechanical axis and the mechanical axis of the tibia. The hip center was obtained using concentric Moose circles 10 .
The pre-operative center of knee was measured by the intersection of the midline between the tibial spines and the midline between the femoral condyles and tip of the tibia. The center of the ankle was determined as the midpoint of the talus. Postoperatively, the center of the knee was determined as the intersection of the midline in the middle of the poly-ethylene inlay and the midline between the condyles of the femoral prosthesis and the tip of the tibial prosthesis 11 . The HKA was defined to be normal between ±3° of the neutral alignment 12; 13 . The mechanical lateral distal femoral angle (mLDFA) was defined as the lateral angle between the mechanical axis of the femur and the distal femoral articulate surface. The mechanical medial tibial angle (mMPTA) was defined as the medial angle between the mechanical of tibia and the proximal tibial joint line (Fig.2.1). The ideal postoperative angle was 90°1 4 .
The posterior distal femur angle (PDFA) was defined as the angle between the femoral posterior diaphyseal cortical bone and the distal femoral cut, The posterior proximal tibia angle (PPTA) was defined as the angle between the tangent to the posterior diaphyseal cortical bone and the tibial plateau. They were measured using published methods 14 ( Fig.2.2). The normal angle was 90°. In addition, the femoral component that was placed unevenly with the distal part of the native femur was defined as malposition of femoral component including over-flexed femoral prosthesis and femoral notch.

Statistical analysis
All data were analyzed using SPSS version 19.0 (IBM   Table 3).
The incidence of femoral notch was 1.3% in the dominant operated side and 9.7% in the non-dominant side. This difference approached but did not reach statistical significance (χ 2 =3.598, P=0.058). The incidence of over-flexed femoral prosthesis in the dominant side was 6.5%, and that in the non-dominant side was 11.1%. There was no significant difference between the two groups (χ 2 =0.948, P=0.330). But the rate of malposition of femoral prosthesis was 7.9% in dominant side compared with 20.8% in non-dominant side. The difference between the two groups was statistically significant (χ 2 =5.083, P=0.024). There was statistically significant difference between the sides for malposition of femoral component.

Total operative time between the sides
The total operative time of the dominant side was (111.8±26.9) min, and the non-dominant side was (113.7±26.1) min. The mean operative time of TKA in the dominant side was shorter than that of the non-dominant side, but the difference between the sides was not statistically significant. (t=-0.422, P=0.674).

Discussion
Our study suggests that there was a significant difference on the sagittal alignment of femoral standing on the side of the operative extremity. They thought this may be related to dexterity or proprioception and should considerate laterality of operative site with respect to surgeon handedness as a factor affecting task performance and outcome. Our study suggested that the malposition rate of sagittal femoral prosthesis in non-dominant side was significantly higher than dominant side. Sagittal plane positioning and alignment of the femoral component were associated with anterior knee pain according to Scott CEH et al's study 17 . However, Hsieh et al. 18 retrospectively analyzed 233 patients accepting primary total knee arthroplasty and found that there was no statistical difference in the bony procedures of tibial resection and femoral cutting between left and right TKA performed by right-handed surgeons. In addition, the thicknesses of the polyethylene were not significantly difference between two groups. They concluded that the right-handed orthopedic surgeons successfully performed TKA procedures to achieve bone resection, soft-tissue balance and thicknesses of the polyethylene between left and right extremity. Further research would be conducted to eliminate the above limitations.

Conclusion
The results of this study suggest that surgeon handedness is likely to be one of factors that